Distance-measuring systems in motor vehicles for supporting parking, in which sensors for measuring distance are arranged on the vehicle, are already known. The sensors are implemented in particular as ultrasonic sensors which send out an ultrasonic signal to an obstacle that is reflected again from the obstacle. The distance between the ultrasonic sensor and the obstacle is then determined from the propagation time. The sensors for measuring distance are preferably integrated in a bumper of the vehicle, so that the distance between the bumper and the obstacle is determined. In measuring, on the one hand, direct measurements may be carried out in which the transmitting sensor itself senses the reflective signal again. On the other hand, cross measurements are also possible in which a different sensor senses the reflected signal. If the obstacle is getting closer to the vehicle, corresponding distance information is output to the driver indicating the obstacle to the driver. Optionally, a warning for the different bumpers or for different sides of the vehicle may in each case be transmitted independently of each other to the driver, so that he/she additionally receives information about the direction from which the obstacle is approaching the vehicle. In general, the minimal distance between the vehicle and the obstacle is calculated and output. Particularly in response to too great an approach to the obstacle beyond a predefined minimum distance, the driver is warned visually and/or acoustically, in order to avoid a collision of the vehicle with the obstacle. On one hand, the minimum distance is a function of the installation geometry of the sensors and their measuring range or their visibility window. Thus, for example, obstacles located very close to the vehicle may lie in a dead angle of the sensor, so that they cannot be detected. Therefore, the minimum distance is permanently predefined and contains a safety distance that helps to reliably prevent a collision of the vehicle with the obstacle. However, if the user makes structural changes on the vehicle, the minimum distance remains unchanged, so that the vehicle may collide with an obstacle without the driver being warned by the distance-measuring device.